(1) Intramembranous charge movements observed in frog twitch and slow muscle fibers are believed to play a role in contractile activation. In twitch fibers, charge movement consists of two components, the main part (QBeta) and a secondary hump (QGamma). As QBeta has been shown to exist in slow fibers, three-microelectrode voltage clamp experiments will be performed on intact slow fibers, or vaseline gap voltage clamp experiments on cut slow fibers, to investigate whether QGamma exists in this fiber type. If it does, its magnitude and kinetics will be compared with those in twitch fibers. Experiments are planned to compare the inactivation properties of QBeta and QGamma in both fiber types. Results from these experiments might give clues concerning the similarities and differences of excitation-contraction coupling mechanism in the two fiber types as well as the mechanism responsible for the lack of mechanical refractoriness in slow fibers. (2) Injection of metallochromic calcium-indicators into twitch fibers have enabled musacle physiologists to monitor the rise in myoplasmic calcium level in the fibers during an action potential or a voltage-clamp pulse. Experiments are planned to apply this optical technique to voltage-clamped slow fibers. A direct comparison of the characteristics of the calcium transient in slow fibers with that in twitch fibers might help us to understand the comparative contractile behavior of the two types of fibers. (3) Simultaneous measurements of charge movement and calcium signal will be performed on both twitch and slow fibers when they are either polarized, chronically depolarized or in the state of fatigue. Pharmacological experiments will also be done to investigate how QBeta, QGamma and calcium signal simultaneously respond to the application of dantrolene sodium, terracaine, dibucaine, caffeine and formamide. The results will hopefully provide a direct link of charge movement to calcium signal, which is just the first step in my long-term project designed to elucidate the complete sequence of events underlying excitation-contraction coupling in normal muscle so that ultimately we can understand that causes the diseases in striated muscles.